"I found that there are 12 million (11,989,322) people aged 65 and above in the UK (Age UK, link below) so let's take that figure and work out 1% of 12 million"
The 1% death rate is for the population as a whole, but the older age groups have much higher death rates
China death rates - but developed countries may be lower - are:
3.6% Age 60-69
8.0% Age 70-79
14.8% Age 80+
However, the government worst case for infection rate is about 50%, so worst case 6 million aged 60+ would be infected, but too little data to say death rate for 60+
Maybe we can very roughly estimate worst case deaths over the whole population of 67 million @ 50% infection worst case rate @ 1% death rate
That's worst case 335,000 EXTRA deaths in the UK
(assuming other deaths wouldn't decrease)